1. Field
Embodiments of the present invention relate to the electronics manufacturing industry and more particularly to a vacuum processing apparatus.
2. Discussion of Related Art
Vacuum processing systems are ubiquitous in microelectronics manufacturing. Many vacuum processing systems include a processing chamber designed for processing a workpiece with a plasma discharge. One such chamber generally includes a first and second electrode arranged in a parallel plate configuration. At least one of the electrodes is powered by a generator typically operating at an industrial RF band. Each electrode is typically a planar, circular disc to be substantially the same shape, albeit of a larger diameter, as a workpiece to be processed (e.g., a semiconductor wafer). It is conventional to pump down the processing chamber to sub-atmospheric pressures (i.e., vacuum) using a vacuum pump coupled to the chamber via a pump port. A process pressure may be controlled to a vacuum level using a gate valve between the chamber pump port and the vacuum pump.
Depending on the configuration of vacuum processing chamber and the location of the chamber pump port, gas conductance within the vacuum processing chamber may be either symmetrical or asymmetrical. Conductance asymmetry is exacerbated as conductance is increased (e.g., high total flow, low chamber pressures, etc.). Conductance asymmetry may limit process uniformity to as low as 10% across the workpiece. For this reason, it is conventional to position the pump port within the processing chamber at a physical location which is symmetrical with respect to the workpiece.
However, it may be desirable to position the pump port asymmetrically within a chamber, for example to one side of a chamber as in the tandem chamber processing apparatus described in U.S. Pat. No. 6,962,644 to Paterson et al. and assigned to Applied Materials, Inc. of California. As such, it may be useful to improve conductance symmetry in such a configuration as well as reduce any cross-talk that could occur between tandem chambers while still maintaining the numerous advantages of the tandem design.